Broadband wireless systems, such as Local Multipoint Delivery/Communication Systems (LMDS/LMCS), represent an effective implementation whereby small and medium sized businesses are able to connect to the ATM backbone without the need for dedicated terrestrial cabling. A LMCS/LMDS typically has a base station connected to the ATM backbone, the base station having a transceiver for point to multipoint communication with network interface units (NIUs) located at customer sites, usually fixed, within a cellular area.
Typically, a base station is located centrally within a substantially circular cellular area. To make better use of the range of radio frequencies which may be licensed to a service provider, and to provide greater coverage, a cell is frequently divided into sectors (for example four sectors each covering 90 degrees) with a sectored antenna operating in each sector.
Network interface units (NIUs) are located at customer sites within each sector and have means for receiving transmission from the base station by way of a point to multipoint protocol. The NIUs connect to customer premise equipment (CPE) via T1 or Ethernet links, for example. Additionally, each NIU will have a highly directional antenna pointed at the base station for bi-directional communication therewith by way of a point to point protocol.
A large metropolitan area will typically be covered by a number of adjacent (overlapping to some degree) cells each having a base station for communicating with customer sites within each cell. Generally, cellular radio access systems used for fixed, bi-directional radio access are interconnected to form a network using radio-based intercell linking or other suitable alternatives such as fiber optics or copper wire. In this way the coverage provided to the metropolitan area can be coordinated.
Traditionally, the multipoint radio access system and the radio intercell links (so called point-to-point radios) were essentially two separate systems. In a radio based intercell link implementation a service provider typically obtains a license for a fixed frequency or frequency spectrum and then uses transmission equipment tuned to a licensed frequency. Therefore, the point-to-point radios for intercell linking are fixed bandwidth units and do not significantly scale in their capacity.